Ring sizer

How to find your ring size on screen

1. Hold any bank, ID or loyalty card to the screen and match the outline to it, then press Save calibration. Every such card is 85.60 × 53.98 mm (ISO/IEC 7810 ID-1), so the page learns how many pixels make a millimetre on your screen. No card? Type the screen’s diagonal instead.
2. Take a ring that fits the finger you are sizing and lay it flat on the circle.
3. Drag the circle’s edge, pinch, or press −0.1 / +0.1 until the circle exactly fills the inside of the band. Look straight down, not at an angle.
4. Read the inside diameter, the circumference and the size in US / Canada, UK / Australia, EU (ISO), Japan / China and India, with the next size down and up in each.
5. No ring to hand? Print the finger strip (A4 or Letter) at 100 %, measure its check line, wrap a strip round your finger and read the millimetres.

Reading the result, with an example

A ring that is 17.3 mm across inside is π × 17.3 = 54.3 mm round. In the table this page uses, the nearest row is 17.32 mm (54.4 mm round): US 7, UK N½, EU (ISO) 54.4, Japan 14 and India 14. The next size down in US is 6¾ (17.12 mm) and up is 7¼ (17.53 mm). US sizes rise by 0.032 in (0.81 mm) of diameter per whole size, so a quarter size is only 0.2 mm across: that is why a millimetre ruler held against a ring is too coarse, and why this page draws to a tenth of a millimetre.

EU sizes follow ISO 8653, which names a ring by its inside circumference in millimetres; the table gives it to one decimal, and shops round it to a whole number (54.4 is sold as 54). UK and Australian sizes are letters with half sizes, about 1.25 mm of circumference apart. India and Japan use whole numbers whose steps are not even, and the table has no India or Japan size at some rows, so the page shows the nearest one that exists.

Tips for a ring that fits

• Fingers swell in heat, after exercise, after salty food and late in the day, and shrink in the cold. Measure a warm hand in the evening, and more than once.
• Wide bands fit tighter. A band about 6 mm wide or more covers more finger, so many people go up a quarter to a half size for it.
• Measure the knuckle if it is wider than the base of the finger: the ring has to pass over it. Choose between the two sizes, nearer the knuckle if the base is much thinner.
• Between two sizes, take the larger. A loose ring can take sizing beads; one that will not pass the knuckle cannot be worn.
• Size the finger the ring is for: the same finger on the other hand is often a quarter to a half size different.

What it cannot do

• It is only as exact as your calibration. On this screen a 1 px mismatch in the card outline moves a 17.3 mm ring’s reading by about 0.03 mm, and one screen pixel on the circle’s edge is about 0.1 mm of diameter. A US quarter size is 0.2 mm of diameter.
• A printer that scales the page makes the strip and the circles wrong, often by 3 % to 6 % (“Fit to page”), which is a whole size or more. The 100 mm check line catches it: if it does not measure 100 mm, print again at 100 %.
• Browser zoom changes the size of everything on the page. The page watches for it and asks you to reset the zoom or recalibrate; moving to another monitor needs a new calibration too.
• Holding a ring on glass adds error of its own: look straight down, because viewing at an angle (parallax) makes the band look offset. A thick ring is hard to read on its inside edge.
• A paper strip stretches and reads small when pulled tight, and cannot tell you how a wide band will feel.
• It is not a jeweller’s gauge. Before an expensive or hard-to-resize ring (an eternity band, tungsten, titanium), try metal sizing rings at a jeweller. It gives the standard scales only, not any one brand’s or shop’s own sizes.

Privacy

Nothing leaves your device and nothing is uploaded. The only thing saved is the calibration, one number of pixels per millimetre with the pixel ratio, in this browser’s local storage under polyatic-ruler. It is shared with the ruler and protractor on this site so you calibrate a screen once; Clear saved calibration deletes it for all three. The PDFs are made in your browser. The page sends an anonymous page-view count and one of two fixed words, ring-size and ring-print, never a size or a measurement.

Where the sizes come from

The size table is the equivalency table of the English Wikipedia article Ring size (revision 1380711691, fetched 23 October 2026): 65 rows, one per US quarter size from 0 to 16, each with the inside diameter and circumference and the UK, East Asia (China, Japan, South Korea) and India sizes. Ring sizing is not perfectly uniform between makers even within one system, which the same article notes for the US scale. The card size is ISO/IEC 7810 ID-1.

Questions

Can I find my ring size online on my screen?

Yes, if the screen is calibrated first. A web page cannot know how big your screen’s pixels are, so hold a bank card to the outline and match it once. Then lay a ring that fits on the circle, make the circle just fill the inside of the band, and the page reads the inside diameter and the size in five systems.

Is an on-screen ring size chart actual size?

Only after calibration. A chart drawn at the browser’s default scale is wrong by 10 % or more on most phones and laptops, which is several whole ring sizes. This chart is drawn from your card calibration, so each circle is the stated inside diameter to within about one pixel.

How do I use the printable ring sizer?

Download the strip PDF for A4 or Letter and print it at 100 % (“Actual size”, not “Fit to page”). Measure the 100 mm check line with a ruler; if it is not 100 mm, the printer scaled the page. Cut out a strip, wrap it round the base of the finger and read the millimetre mark where the 0 end meets the scale. That number is the circumference; page 2 converts it to every system.

What is my ring size in mm or cm?

A ring size in mm is either its inside diameter or its inside circumference. ISO 8653, used for EU sizes, names a ring by its inside circumference in mm: US 7 is 17.32 mm across inside and 54.4 mm round, so it is EU 54.4, which shops usually sell as 54. Divide by 10 for cm.

How do UK and India ring sizes compare with US sizes?

They are different scales for the same inside size. From the table this page uses: US 7 is 17.32 mm inside, which is UK N½, EU 54.4, Japan 14 and India 14. US sizes go up in steps of 0.8 mm of diameter, UK letters in about 1.25 mm of circumference, and India and Japan numbers in uneven steps.

What if I am between two ring sizes?

Take the larger one, especially for a wide band or a knuckle wider than the base of the finger. A ring slightly too big can take sizing beads or a guard; one that will not pass the knuckle cannot be worn.